Vaccine Supply May Miss Swine Flu Peak

By DONALD G. McNEIL Jr.

Published: September 12, 2009

Several prominent epidemiologists are warning that even though the new swine flu vaccine works much better than expected, it will still come too late to blunt the peak of this season's pandemic.

The epidemiologists said Friday that they expected the peak to come as early as next month, long before enough vaccine to protect all 159 million Americans who need it most will be ready.

''It would be bizarre for it to peak in January or February, the way seasonal flu does,'' said Dr. Marc Lipsitch, an epidemiologist at the Harvard School of Public Health and a consultant on flu epidemics to the President's Council of Advisors on Science and Technology.

Dr. Lipsitch noted that the pandemics of 1918 and 1957, which were also caused by new viral strains, had both peaked early. Influenza cases are usually near zero at this time of year, but Friday's weekly report from the Centers for Disease Control and Prevention rated flu activity as ''widespread'' in 11 states, mostly in the Southeast but also in Arizona, Alaska and Oklahoma. (Widespread is the highest of five levels.)

Dr. Anne Schuchat, the agency's chief of immunization and respiratory diseases, said 98 percent of those flu cases were the new H1N1 swine flu.

On Thursday, federal officials reported that one dose of the new vaccine, rather than the two they had expected, appeared to fully protect recipients against swine flu. They said that meant there would eventually be plenty of vaccine for everyone given first priority for shots: health care and emergency workers, pregnant women, everyone ages 6 months to 24 years, adults up to age 64 with medical problems, and people caring for infants under 6 months old.

The officials expect about 50 million doses of swine flu vaccine to reach government warehouses by Oct. 15, and 20 million more to be ready each week after that until 195 million is reached.

Then those lots must be shipped to health centers, schools and other vaccination sites, people must be injected, and each must develop immunity. Immune responses are different in each individual, but the clinical trials suggest that most will be protected after 8 to 10 days.

So if the epidemic's peak comes in late October, millions of people are likely to catch the flu before the vaccine is available.

''A month would have made a huge difference,'' said Ira M. Longini Jr., an author of a report by an epidemic-modeling team at the Fred Hutchinson Cancer Research Center in Seattle and the University of Washington.

If one shot turns out to be protective in children and if the flu peaks in late December, as the 1968 Hong Kong flu did, ''we could be O.K.,'' Dr. Longini said. ''But that's a lot of ifs.''

In response, federal officials said there was no way to tell whether the pessimistic models would be right, since flu peaks at different times in different regions each year.

''I can't tell you it's going to be too late for 'a lot' of people,'' said Dr. Anthony S. Fauci, who is in overseeing vaccine trials for the National Institutes of Health. ''It's certainly going to be too late for some.''

In any event, most cases are expected to be mild. The virus has not changed significantly since the spring and, while a few cases of strains resistant to the antiviral drug Tamiflu have been detected, they have not yet become widespread.

Dr. Fauci said Friday that the trials he was overseeing confirm that one dose usually created immunity in adults. In the elderly, only 50 percent to 60 percent develop it, he said, but that is ''right in the ballpark'' for seasonal flu shots in the elderly, since their immune responses are weaker.